Gallacher, U.S. Pat. No. 4,018,865 and copending U.S. patent application Ser. No. 785,069, filed Apr. 7, 1977, now allowed, describes the use of water-immiscible organic solvent solutions of alkyl aromatic sulfonic acids alone or in combination with an .alpha.-hydroxy oxime for the separation of difficult to separate metal value pairs in acidic aqueous media.
In Gallacher and Rydzik copending U.S. patent application Ser. No. 892,327, filed Mar. 31, 1978, now allowed, it is disclosed that the selective extraction efficiency of the foregoing solvent-extractants can be improved by the addition of a fuzed ring aromatic N-alkyl triazole.
Fuzed ring aromatic triazoles, alkylated on the aromatic ring with, e.g., C.sub.4 -C.sub.16 alkyl groups, are known from Netherlands Pat. Publication No. 6,414,144; U.K. Pat. No. 1,065,995 and Bridger et al., U.S. Pat. No. 4,060,491. Claim 1 of U.K. Pat. No. 1,065,995 shows substituted 1-H benzotriazoles having the formula: ##STR1## wherein R is a straight- or branched-chain alkyl group containing from two to twenty carbon atoms. In U.S. Pat. No. 4,060,491, 5-alkylbenzotriazoles, wherein the alkyl group contains from 4 to 16 carbon atoms, are disclosed to be useful anti-wear additives for lubricants. The foregoing applications, publications and patents are incorporated herein by reference.
It has now been discovered that 5-alkyl benzotriazoles are excellent in their own right as solvent-extractants for selectively separating metal values. Moreover, the selective extraction efficiency of such 5-alkyl benzotriazoles can be improved by the addition of acidic compounds, such as alkyl aromatic sulfonic acids, dialkyl phosphoric acids and/or carboxylic acids. In addition, such solvent-extractants are uniquely adaptable for use in processes wherein the kinetics of separation and stripping are enhanced with additives such as 1-alkylbenzotriazole, and/or by using higher than the usual temperatures for extraction and stripping. These advantages will become apparent from the Examples hereinafter set forth.